As title suggests.
Coming home the other day I find my PC started to restart out of nowhere, with no warning before or errors afterwards. I haven't changed anything and haven't had this problem before.

Any suggestions on what to do?

Device specs:
Processor Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz 3.60 GHz
Installed RAM 64.0 GB
Storage 233 GB HDD ST9250315AS, 112 GB SSD OCZ-VERTEX2, 466 GB SSD Samsung SSD 970 EVO Plus 500GB
Graphics Card NVIDIA GeForce RTX 3060 (12 GB)
System Type 64-bit operating system, x64-based processor
OS Windows 10

UPDATE: Memtest got through 2 out of 4 passes in under 4 hours before I got fed up with waiting, which in itself seems a good sign since it didn't restart there.
Event viewer showed one odd Event: The process C:\WINDOWS\Explorer.EXE (ANDROID-17) has initiated the restart of computer ANDROID-17 on behalf of user ANDROID-17\smuld for the following reason: Anderer Grund (geplant) Reason Code: 0x80000000 Shut-down Type: restart Comment:

No idea why because automatic restart is disabled.